The management of fractures and injuries to the extremities has a long and colorful history in medicine. Prior to the invention of plaster of Paris by the Flemish army surgeon Mathijsen in 1852, the stabilization of broken bones and sundry joint injuries was a haphazard affair using pieces of wood, branches, and any rigid material that might be available. Plaster of Paris was rubbed into muslin or linen cloth prior to its use, “a tedious process”, and wrapped around an injured limb to provide stability. When the anhydrous calcium sulfate was recombined with water, the reaction produced the slow drying, but stiff gypsum. Manufactured rolls of plaster of Paris cast material were not available until the mid-1900's. The casts made in this way were messy to apply, often extremely bulky, could be very difficult to remove, would break down with walking, fell apart in water, were heavy, and made visualization of a fracture difficult with x-ray. Yet at the time they were a major step forward in the medical management of these unstable musculoskeletal injuries.
Plaster casts were used consistently and devotedly until the 1980's when fiberglass materials became available. Though more expensive and somewhat more difficult to work with, fiberglass soon became the preferred casting material in many clinics and hospitals and remains so today. It offered increased lightness, somewhat better visibility under x-ray, and was resistant to softening if wet. Unlike plaster rolls or strips which could remain open on the shelf, fiberglass would gradually harden if exposed to air and needed to be packaged in airtight bags. Fiberglass still required water activation to harden into a usable cast, and was highly user dependent in the quality of the final product. It has sharp edges, folded corners can produce skin ulcers, and it can be more difficult to remove than plaster. It is available in rolls of various sizes (2″, 3″, 4″, 5″, & 6″) A cast saw with a good blade is necessary for its removal. Fiberglass and plaster remain the most commonly used material casting in orthopedics today.
A variation on fiberglass is the Delta-cast brand (distributed by BSN Medical) of roll fiberglass casting tape material that is more pliable and less rigid than fiberglass, has improved radiolucency and can be cut with a scissors as well as with a cast saw. It comes in rolls similar to fiberglass and is wrapped around the injured extremity over a cotton or fabric padding under-layer in the same fashion as plaster and fiberglass. It too is water activated. It is slightly more expensive than fiberglass, but has advantages of comfort and enough flexibility to be removed in some instances.
For the purposes of this discussion it is important to define splints, casts, and braces. While these are all used to support body parts, they are separate and distinct products, each constructed differently and for disparate uses.
Splints are typically rigid supports made of various substances, plaster, fiberglass, plastic, metal or inflatable materials, which temporarily support an injured extremity. They often are applied to only one surface of a limb and may be held in place by an elastic bandage, hook and loop, or other wrapping. They generally do not rigidly encircle a limb to allow for swelling in the early stages of an injury. Typically they are applied in an emergency setting, worn for less than a week, are discarded after transition to a more long term support system when seen in an orthopedic clinic. One common material used for splints is Ortho-Glass distributed by BSN Medical. This material is a limp fiberglass material impregnated with water activated resin and covered with a non-woven fabric. It is wetted and held to the body with elastic bandage while it cures in a few minutes.
Braces are usually employed as a removable, sometimes hinged, device to provide stabilization to a joint in which bones or ligaments may have been injured or for several weeks after removal of a cast to provide additional support during recovery of range of motion (ROM) and strength. Cast braces are an addition hybrid support system (Air Cast Walking Boot, CAM walkers, Sarmiento elbow brace) which typically utilize a rigid shell or strut system with a padded liner and may be removable depending on the nature of the injury (elbow dislocations, some stable ankle fractures, etc.) Materials such as Orthoplast distributed by BSN Medical and similar low temperature thermoformable plastic sheets are sometimes used for braces. These single layer plastic sheets material are heated in hot water to become formable and usually custom cut and formed in situ (in place on the body). Wrap closures are then added such as hook and loop, tape or bandages are used to secure them to the body.
Casts are typically a circumferential protective shell of plaster, synthetic composites, or fiberglass that will maintain the alignment of an injury. They may be worn for upwards of 3-12 weeks depending on the characteristics of the injury involved and the healing qualities of the patient. Currently, the vast majority of casts are assembled “in situ” (on the body) in a process where rolls of material, both padding and a wetted plaster or fiberglass resin layer, are successively wrapped circumferentially around the body part in multiple layers. Once completed, they completely encircle the body part in a continuous fashion that becomes rigid to some degree once the catalyst sets and typically can not be opened or adjusted without cutting through the layers of material.
The prior casting systems are designed to be constructed from multiple separate materials. This requires the practioner to be skilled in utilizing these materials and applying these materials, such as plaster, fiberglass or Delta-cast to create the cast on the patient. Also, the padding must be applied initially before the casting material is applied. Any problems with either of the materials require the entire process to be restarted.
Another disadvantage of these systems is that they require multiple layers of material to complete the process and are time consuming to apply. Padding is necessary to protect and cushion the limb from the hard cast material, to allow a margin of room for swelling yet be applied closely enough to stabilize and maintain the reduction of the fracture. The padding also provides an interface so that when the cast saw is used to cut the cast for removal, it does not directly contact, abrade, or cut skin. Typically, a cotton or fabric stockingette is applied directly to the skin over which are wrapped multiple layers of synthetic cast padding. The cast material (plaster, fiberglass, Delta-cast) is then applied by wrapping over this padding in multiple layers to provide the hard shell as an exoskeleton to stabilize the extremity. Typically, a short arm cast (SAC) will require 2 rolls of cast padding and 2-3 rolls of 2″-3″ fiberglass. A short leg cast (SLC) will use 3-4 rolls of cast padding and 3 rolls of 3″ or 4″ fiberglass. Pediatric casts can be difficult to apply properly and it is important that they not be too tight or too loose. Too few layers and the cast will buckle or bend, too many and it will be unnecessarily cumbersome. If the plaster or fiberglass has a pressure point or a hard edge it can result in a skin ulcer. If the entire cast is applied too tightly or the extremity subsequently swells inside the cast, the blood flow to the extremity can be compromised resulting in an ischemic limb, one of the most feared of all cast complications. As such, many surgeons and orthopedists will split a cast immediately after application to allow for some degree of swelling for several days in the immediate post-injury or post-surgical period. Proper cast application is recognized as an art. It is extremely user dependent in terms of the quality of the cast which results. This has significant ramifications in terms of fracture care outcomes, overall patient safety and cost.
A major disadvantage of the existing systems is the need for the materials (plaster, fiberglass, Delta-cast) to be immersed in water in order for an exothermic reaction to occur which will activate the hardening or curing process. Plaster or fiberglass splint or cast application requires a systematized set-up of the proper supplies and adequate preparation. This can be messy and inconvenient, and typically results in the cast padding becoming sodden with water which then must dry over time. The temperature of the water affects the length of time necessary for the cast material to cure or harden. Colder water slows the process and requires prolonged pressure or molding of the cast on the patient's extremity, while warmer water will cause the material to set more quickly, produces more heat against the skin, and if the practitioner is not adept at casting may result in hardening prematurely before the layers of cast material have been completely applied or molded. This is at once a messy, time consuming, and often times uncomfortable process for the patient. One can imagine that if one has a fracture of a long bone, such as the tibia, radius, or ulna, that any unnecessary or prolonged manipulation of the extremity will not be appreciated by the patient.
In addition, most fractures require the practitioner or physician to “reduce” (align) the broken bone so that it is in optimal anatomic position at the end of the casting application procedure before the cast fully hardens. This can be very frustrating if the resin begins to set prematurely or if anatomic alignment is difficult to maintain. If acceptable alignment is not achieved (typically confirmed by a post-casting x-ray), the cast must be cut off and the procedure repeated until an acceptable reduction is attained.
Another disadvantage of these systems is that because of sticky resins in the fiberglass, the practitioner almost always must use latex or rubber gloves to protect the hands. The patient must be draped to protect them from the sticky resin and considerable time and expense is incurred in this protection and the resulting clean up procedure. Gloves are typically used for plaster application as well due to the caustic and drying effect on skin of prolonged contact with plaster and water and the resulting mess and clean up are even more considerable.
Another disadvantage of plaster and fiberglass is the reduced visibility of the bones and soft tissues when diagnostic x-rays are obtained to follow the healing of the fractured injury over subsequent weeks. If the cast is irregular in its application, with varied thickness of the cast material, this may significantly affect visualization of the injury site. Radiology reports in which casts overlay fractures typically say, “Cast material obscures fine detail” as a disclaimer in their official dictations. Often the new bone or callus which forms at the site of a fracture is difficult to see and may be easily obscured by cast material. If a fracture is not healing properly, and a mal-union or non-union is occurring, surgery may be indicated. To remove the cast prematurely may allow the fracture to displace, to keep it on longer than necessary is not conducive to good patient care. A product which allows unimpeded x-ray visualization of a fracture would be an improvement of major significance.
Another disadvantage of plaster and fiberglass casts is that the outer layer is usually rough, hard and abrasive to other parts of the body. Sleeping can be a particularly uncomfortable experience as the hard abrasive surface quickly causes irritation as it touches other body parts, is laid on, or rubbed across the skin when rolling over.
A significant disadvantage of both plaster and fiberglass casting material is the need to use a “cast saw” for removal. These are made by a number of manufacturers but are characterized by having an oscillating curved blade which the patient is told “can't cut you.” Rather it won't cut, unless the operator drags it along the skin rather than pressing down and then lifting out of the cut with an “up and down movement” to the next point of application. Unfortunately, synthetic material casts, like fiberglass, increase the chance for skin irritation, burns, and cuts. Synthetics produce heat in the cast saw blade more rapidly than plaster. Perhaps more disconcerting, they are uniformly noisy with a metallic rasp that is unnerving to most patients and especially to children. One of the more notable pediatric orthopedic texts observes: “Few things in medicine are as barbaric as a cast saw and a screaming child in the middle of the night.”
Another problem with prior systems such as plaster or fiberglass is the need to completely remove the cast if it is too tight, broken, worn, the fracture needs alignment, or the cast padding gets wadded up inside the cast thus creating a pressure point. Some surgeons are adept at “wedging” casts, but in general plaster and fiberglass casts are not re-moldable or alterable once they have hardened. It is easier and safer to replace it, however time consuming or expensive. This is a common cause of emergency room visits and is a not insubstantial cost to the health care system.